The Securities and Exchange Commission plans to move into a new downtown Washington headquarters within the next 18 months, ending a 10-year search for a home for its 1,450 Washington-area employes.

The move also would mark the end of the lengthy battle between the agency and the federal government's landlord, the General Services Administration, over the right to lease office space.

The reconciliation of the squabbling sister agencies was engineered last month by the House Public Works Committee, SEC officials say, just as Congress was about to make the SEC the second major federal agency to get its own leasing powers.

The Federal Communications Commission last year won congressional approval to bypass GSA in finding a new headquarters building for its 1,700 employes. The FCC is now proposing to leave downtown Washington -- although its charter requires it to be headquartered in the District -- and is negotiating to move into a controversial high-rise office building in Rosslyn.

The Rosslyn location, the 30-story Twin Towers complex, has been sharply criticized by two other federal agencies -- the Interior Department and the National Capital Planning Commission -- for allegedly marring Washington's skyline. Construction of the buildings -- to be the tallest in the Washington area when completed -- was fought unsuccessfully in federal court.

Legislation approving the FCC move to Arlington, already passed by the House in a rider to the 1981 appropriations bill, is scheduled to come up in the Senate in the next few days.

Despite FCC claims that General Services has been incapable of finding it office space in downtown Washington, one high GSA official, John Guluardi, said yesterday that, "There are many buildings now coming on the market in downtown Washington, and we're looking to lease space in them for the SEC and numerous other agencies. The FCC could have been one of them."

A solicitation for bids to provide 320,000 square feet of office space for a new SEC headquarters will be published by GSA within the next few days.

"We've been in the same place [500 N. Capital St.] for 15 years and been asking GSA for additional space for 5 to 10 years," SEC executive director Benjamin Milk said yesterday.

"They had not been responsive to our needs to consolidate and the whole thing ended in the fiasco at Buzzard Point,", Milk said. GSA leased a remote office building on Buzzard Point on the north bank of the Anacostia River to which several other federal agencies refused to move. FBI and Defense Department employes are now there.

Suddenly this summer the GSA became responsive, Milk said, "and in the last three months they've done more than has been done in the past 10 years. We don't have and don't want our own leasing authority," he said, particularly because "we don't have the expertise... the time and employes, and don't want to hire consultants" to find new office space.